For rendering of 3D graphics, for games or the like, in conjunction with an increase in resolution of a display apparatus, there is a tendency for screens that are rendered to have an increase in pixels. Because a calculation amount for rendering of a screen increases in proportion to the number of pixels, in particular, rendering of a screen corresponding to content such as that for which a real-time capability is requested requires optimization.
In recent years, there are cases in which rendering of a screen is optimized by using a plurality of GPUs. In patent document 1, by classifying GPUs that render in accordance with a z-value of a rendering object, and composing images of the respective rendered rendering objects referring to the z-value, a screen that is a final output is generated. More specifically, in a case of rendering one screen by four GPUs as illustrated in FIG. 5, each GPU outputs an image that has rendered a rendering object having a respectively different z-value, and a z-buffer indicating a z-value of each pixel in the image. A composing unit then generates a final output screen by performing a z-value comparison of z-buffers corresponding to these images and composing so as to employ, for each pixel, the pixel of the rendering object that is present the most at the front.